Two adjacent nitrogen atoms linked by one alkylene unit and one carbonyl moiety form a cyclic alkylene urea. When alkylene is ethylene, an ethylene amine (EA) in which two nitrogen atoms are linked intramolecular by a carbonyl moiety
is here referred to as an UEA. Replacing the carbonyl bridge with two hydrogen atoms yields the corresponding ethylene amine. For example: EU↔EDA, UDETA↔DETA, UAEEA↔AEEA, UTETA↔L-TETA, UTEPA↔L-TEPA. Some higher amines host more than one carbonyl moiety, e.g. DUTETA the diurea of L-TETA. The carbonyl moiety may link nitrogen atoms on two separate molecules. For example H2NC2H4NH—CO—NHC2H4NH2 and replacing the carbonyl moiety with two hydrogen atoms here yields two EDA. As to naming of the molecules, EDA stands for ethylenediamine, DETA for diethylenetriamine, TETA for triethylenetetraamine, TEPA for tetraethylenepentamine, PEHA for pentaethylenehexamine, AEEA stands for aminoethylethanolamine. When there is a single cyclic urea in the molecule this is indicated by adding a U in front of the name, e.g. UTETA means the cyclic urea of TETA, while when there are two cyclic ureas in the molecule this is indicated by DU, i.e. DUTETA means the internal cyclic diurea of TETA. If there is a number indicated for the U this refers to the amino group where the U group is located. There is one exception to this naming and that is that instead of UEDA the abbreviation EU is used, which stands for ethyleneurea.
Aqueous solutions of alkylene and alkanol amines are commonly used in reversible CO2 absorption processes. On absorption a range of compounds are formed such as carbonates, bicarbonates, carbamates and alkylene ureas. Desired products are those that readily desorb CO2 on heating. Cyclic carbamates and ureas are undesirable owing to their high stability.
U.S. Pat. No. 4,650,906 and JP 60126248 disclose the decarboxylation of ethylene amine carbonates by heat treatment and distillation. Examples of carbonates disclosed are those of diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), and piperazine (PIP). JP 60120842 discloses besides thermal treatment also the addition of a hydroxide-containing base. None of these two documents discloses cyclic alkylene ureas or a conversion thereof to give the corresponding alkylene amines.
U.S. Pat. No. 4,683,337 discloses the conversion of ethylene amines to linear carbamates by reacting them with CO2 followed by decarbonating and dehydrating them to recover the amines. US '337 does not disclose the formation of cyclic alkylene ureas.
The process of the present invention as indicated is about converting cyclic alkylene ureas into their corresponding alkylene amines, more in particular it is about removing the carbonyl group of a cyclic alkylene urea to give the corresponding alkylene amine according to the following general reaction scheme:

U.S. Pat. No. 4,387,249 discloses the reaction of ethylenediamine (EDA), ethanolamine (MEA) and urea to give aminoethylethyleneurea (UDETA) and ethyleneurea (EU) that after hydrolysis gives DETA and EDA. The hydrolysis is said to be done in the presence of a Brønsted base, but the only one specifically mentioned is sodium hydroxide.
U.S. Pat. No. 4,503,250 discloses the hydrolysis of a product mixture obtained by the reaction of an amine or ammonia with an alcohol in the presence of carbonic acid derivatives. In the examples work-up of the reaction mixture is performed using 50% aqueous KOH under reflux overnight. In the examples of '250 it can be seen that the yield of alkylene amines obtained by treating the reaction mixture with KOH is low and subject to improvement.
The use of caustic bases as disclosed by the prior art documents to remove the carbonyl group from cyclic alkylene ureas also has as a disadvantage that it results in low product selectivities due to degradation of the desired products. In addition, when using an (inorganic) base, salts are formed as by-products which complicate the following separation of organics, resulting in lower yields of the targeted product. In addition the combination of amines, water, salt and high temperatures can cause problems with corrosion, discolored products and decreased storage stability. Salt generation also creates waste.
The present invention provides a process in which the above problems are solved.
The present invention relates to a process to convert cyclic alkylene ureas into their corresponding alkylene amines wherein the process is performed by reaction with an amine compound and wherein the amine compound is a primary amine, a cyclic secondary amine or a bicyclic tertiary amine.
Unexpectedly, it was found that amines, which are much weaker bases than the inorganic caustic bases hitherto disclosed, are effective in converting cyclic alkylene ureas into their corresponding (linear) alkylene amines at high yields of the desired alkylene amine products and that degradation of the alkylene amines is minimized. It was also found that only certain amines are effective and that the chemical nature of the amine is critical to the function and not the basicity by itself, which shows that the mode of function is distinctly different from that of caustic bases like NaOH and KOH.
Unexpectedly, when using the amines of the present invention to convert cyclic alkylene ureas into their corresponding alkylene amines, the degradation of the alkylene amines is to a large extent avoided, and a much better yield of the desired alkylene amines is provided. It is believed that in the process of the invention the amine reactant does not primarily act as a base but as a nucleophile which makes the process distinctly different from the prior art processes using caustic for the conversion. Furthermore, the process of the invention is much less critical on dosing reactants because the amines are in embodiments, for example embodiments wherein water is present, not consumed by the process and additionally the process of the present invention has as an advantage that water needs not be added in all embodiments, such as for example when alkylene and alkanol amines are employed and the respectively obtained cyclic alkylene urea and cyclic alkylene carbamate can be recovered as products. In many embodiments it is possible and advantageous to use reactive separation steps, for example reactive stripping or reactive distillation, to separate the alkylene amine from the cyclic alkylene urea in order to further the reaction to the product side, which process steps would be less desirable in the presence of hydroxides as heating reaction mixtures rich in hydroxides easily gives corrosion.
It should be noted that U.S. Pat. No. 4,514,379 discloses a catalytic process to convert oxazolidinones into alkanol amines by using a small amount of amine, preferably the alkanol amine precursor of the oxazolidinone. It is said that the use of a catalytic amount of amine will reduce or eliminate the need for a long induction period when using water without an inorganic base and it is suggested that waste is avoided in comparison to using an inorganic base. It is nowhere disclosed or suggested that the use of amines increases yields by preventing the formation of degradation products. Converting cyclic carbamate functionalized compounds into an alkanol amine is much easier than converting a cyclic urea functional compound into an alkylene amine, as cyclic carbamates are much more reactive and—in contrast to cyclic ureas—can be efficiently hydrolyzed with water alone. This would clearly lead someone to believe that using amine compounds for converting ureas would be an unacceptable alternative.
In a preferred embodiment in the process of the invention the cyclic alkylene urea that is subjected to the conversion to give a corresponding alkylene amine are:
Wherein R1 and R2 each independently are chosen from the group of hydrogen, an alkylene amine group of the formula X—R3—(NH—R3—)p—, or an alkoxy group of formula X—R3—(O—R3—)n—, or a group combining such alkylene amine and alkoxy units p and n, wherein one or more units ˜N—R3—N˜ may be present as either one of the rings
and wherein each R3 independently is as defined below and X may be hydroxyl, amine, a linear or branched C1-C20 hydroxyalkyl or C1-C20 aminoalkyl group, n and p independently is at least 1, preferably 2-20, optionally containing one or more piperazine, or alkylene urea groups, or when p or n is 0 may be a C1-C20 hydroxyalkyl or C1-C20 aminoalkyl, and R3 is alkylene or substituted alkylene.
In a preferred embodiment R2 is a hydrogen atom and R1 is not a hydrogen atom.
In a more preferred embodiment R2 is a hydrogen atom and R1 contains a repeating alkylene amine group, even more preferably a repeating ethylene amine group of the formula X—(NH—C2H4)n wherein optionally one or more units NH—C2H4—NH may be present as one of the rings
and wherein n is 1 to 20, and X may be a hydrogen atom, an aminoalkyl, an hydroxyalkyl, N-imidazolidinonealkyl or piperazinoalkyl group, most preferably wherein the alkyl is ethyl.
R3 is preferably ethylene or propylene, optionally substituted with C1-C3 alkyl substituents. More preferably it is an unsubstituted ethylene or propylene, most preferably ethylene.
Some examples of cyclic alkylene ureas that are most preferred are EU (ethyleneurea), UDETA (the urea of diethylenetriamine), UTETA (the ureas of triethylenetetraamine, i.e. U1TETA or U2TETA, dependent on whether the urea is between the 1st and 2nd amine in the chain or 2nd and 3rd amine, respectively), DUTETA (the diurea of triethylenetetramine), DUTEPA (the diurea of tetraethylenepentamine) or any mixture of these. The molecular structures of the above cyclic alkylene ureas are given in the FIGURE.
The amine compound can be a primary amine, a cyclic secondary amine or a bicyclic tertiary amine. Primary amines are amine functional compounds in which the amine group is of the formula R4-NH2 and wherein R4 can be any organic group, preferably an aliphatic hydrocarbon with optional heteroatoms such as oxygen and/or nitrogen. Secondary cyclic amines are amines of the formula R5-NH—R6, wherein R5 and R6 together form a hydrocarbon ring, optionally with heteroatoms such as oxygen and/or nitrogen, preferably a piperazine ring. Tertiary bicyclic amines are amines of the formula R7-N(—R9)-R8 where R7 and R8 together form a hydrocarbon ring—optionally with heteroatoms such as oxygen and/or nitrogen—and R7 and R9 together form another hydrocarbon ring—optionally with heteroatoms such as oxygen and/or nitrogen. On all the above groups R4 to R9 substituents can be present, like alkyl or hydroxyalkyl groups. Primary amines, cyclic secondary amine and bicyclic tertiary amines all contain a sterically relatively unhindered amine group. In this document a compound is defined as a primary amine or a secondary cyclic amine or a tertiary bicyclic amine if one of the amine groups in the compound is a primary amine or secondary cyclic amine or a tertiary bicyclic amine group, independent of if this compound contains further amine groups that may be different in their nature. A compound can also contain two or more different amine functionalities, e.g. a primary amine and a secondary cyclic amine functionality or a primary amine, a secondary cyclic amine and a tertiary bicyclic amine functionality.
Preferred examples of primary amines are alkylamines, linear ethylene amines, and alkanolamines. Preferred examples of cyclic secondary amines are amines that contain a terminal piperazine ring. Preferred examples of bicylic tertiary amines are 1,4-diazabicyclo[2.2.2]octane (DABCO), 1,4-diazabicyclo[2.2.2]octan-2-yl)methanol and 1-azabicyclo[2.2.2]octane (Quinuclidine). Structures of some of the amine compounds are given in the FIGURE.
The amine compound is preferably a compound with more than one amine group wherein at least one of the amine groups is a primary amine, even more preferably it is an amine wherein two amine groups are a primary amine. The amine compound is preferably a compound different than R1-NH—R3-NH—R2 that is obtained by the process of the invention.
In another preferred embodiment the amine compound is a compound that can bind with the carbonyl group from the cyclic alkylene urea (CAU). Preferred amine compounds include an alkylene amine, or an alkanol amine compound, even more preferably a smaller alkylene amine, ethylene amine, or alkanol amine, ethanolamine, than is formed by the process of the invention, most preferably EDA or DETA, MEA, aminoethylethanolamine (AEEA), N-aminoethylpiperazine (AEP), N, N′-diaminoethylpiperazine (DAEP), UDETA, N, N′-diaminoethyl-2-imidazolidinone (U2TETA), tris-aminoethylamine (TAEA). Many of the above compounds are shown in the FIGURE.
In yet another preferred embodiment the amine compound is a compound that binds the carbonyl group from the cyclic alkylene urea to give among others another linear or cyclic alkylene urea or linear or cyclic alkylene carbamate, that is larger or less volatile than the alkylene amine formed by the process of the invention, even more preferably an ethylene amine that is solid under the conditions used to work up the reaction mixture or an ethylene amine bound to a solid carrier. Examples thereof are DETA-PS (i.e. a diethylene triamine linked to a solid polystyrene) or a solid polyethyleneimine (PEI).
The process of the present invention can be done with or without any additional liquid present. If a liquid is added to the reaction system, the liquid preferably is a polar liquid, such as an alcohol or water. Doing the process of the present invention in the presence of water as a liquid or without any liquid is preferred. Since in some preferred embodiments the amine compound will react to yield another, in preferred embodiments less stable, urea or carbamate compound, having water present during the reaction can have the additional benefit that the newly formed urea compound can be hydrolyzed with water to release its carbonyl group which can then be recycled into the process or separated off, for example as carbon dioxide or a ionic derivative thereof (such as hydrogen carbonate or carbonate salt).
The amine compounds that are preferably used when the reaction is done in the presence of water are ethylenediamine (EDA), N-methylethylenediamine (MeEDA), diethylenetriamine (DETA), ethanolamine (MEA), aminoethylethanolamine (AEEA), piperazine (PIP), N-aminoethylpiperazine (AEP), 1,4-diazabicyclo[2.2.2]octane (DABCO), 1,4-diazabicyclo[2.2.2]octan-2-yl)methanol, triethylenetetramine (TETA), N-diethyldiamine-2-imidazolidinone (U1TETA), N,N′-diaminoethylpiperazine (DAEP), N,N′-diaminoethyl-2-imidazolidinone (U2TETA), tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), and the mono cyclic ureas of TEPA and PEHA (i.e. U1TEPA, U2TEPA, U1PEHA, U2PEHA, U3PEHA) and the dicyclic urea isomers of PEHA (i.e. DUPEHA), a polyethyleneimine (PEI) or an alkylene amine on a solid carrier.
In a further preferred embodiment the released carbonyl group, i.e. often carbon dioxide, is continuously removed from the process which will enhance the process. The carbon dioxide can be removed for example by working in a suitable reactor unit comprising or connected to a section for actively removing CO2 by desorption, for instance by distillation, stripping or flashing, with or without a membrane.
In preferred embodiments the above subsequent step of hydrolyzing a potentially formed cyclic or non-cyclic urea to releasing carbon dioxide is performed by at least a step in which the materials are stripped. A person skilled in the art will know that such a stripping step is suitably done by having a sufficiently high flow of carrier gas and by ensuring good mixing and proper gas to liquid contact so that the maximum amount of carbon dioxide is removed from the system, in any way, the carbon dioxide should be so removed or isolated that it will not recombine with the amine compound with which it originally formed the cyclic urea, or any other amine compound.
In another preferred embodiment of the invention the amine compound or any urea compound formed from the reaction between the amine compound and the cyclic urea compound are recycled back into the process or separated off.
The process of the invention is preferably done at a temperature of at least 150° C., preferably at least 200° C., more preferably at least 230° C., and most preferably of at least 250° C. Preferably the temperature during the process does not exceed 400° C., more preferably 350° C.
The process of the present invention is in embodiments is performed for a time of between 1 minute and 12 hours. Preferably the reaction is run in less than 10 hours, more preferably in less than 8 hours, most preferably less than 5 hours. As a skilled person will understand this reaction time does not include any further processing of the reaction mixture such as for separating the obtained compounds.
The process can be carried out in a batch reactor, possibly fed-batch operation, or in a continuously operating system such as in a cascade of continuous flow reactor. The reaction and separation can be performed in separate steps or at least partially simultaneously.
In the large-scale production of chemicals it is preferred to employ a continuous process. The continuous process may be, for example, a single-pass or a recycle process. In a single-pass process, one or more of the reagents pass through the process equipment once, and then the resulting effluent from the reactor is sent for purification or further processing.
In such a scheme, the cyclic alkylene urea, amine compound and possibly water may be fed to the equipment as desired at a single point or at multiple points throughout the process equipment, which may include continuously stirred tank reactors, tubes, pipes, reactive distillation columns, reactive stripping units or combinations thereof.
The person skilled in the art is capable of selecting the proper reactor and separation unit scheme by determining the overall yield, energy consumption and waste production.
The amine compound is preferably dosed in a molar amount of between 0.001 and 100 equivalents in regard to the total molar amount of CAU, more preferably between 0.01 and 50 equivalents, even more preferably between 0.05 and 30 equivalents, yet more preferably between 0.15 and 25 equivalent and most preferably between 0.20 and 20 equivalents.
In a most preferred embodiment a cyclic alkylene urea of TETA or TEPA, such as linear TETA diurea (DUTETA) or linear TEPA diurea (DUTEPA), is converted to linear TETA (L-TETA) or linear TEPA (L-TEPA) by employing EDA, DETA, MEA, AEEA, N-methyl EDA (MeEDA), AEP, DAEP, U2TETA, TAEA with or without added water.
Particularly preferred are the amine compounds EDA, DETA, U2TETA, DAEP or AEP when doing the reaction in the presence of water
The conversion of DUTETA with EDA and water proceeds preferably between 150 and 350° C., preferably between 200 and 300° C.